LinearLayout设置android:animateLayoutChanges=true在ViewPager2中不生效问题

问题根因 #

• ViewPager2默认属性transitionGroup=true，会拦截所有子View层级的布局过渡动画，直接导致XML配置的android:animateLayoutChanges属性失效
• 嵌套在ViewPager2内部的RecyclerView，系统为了避免页面切换动画和列表item动画产生冲突，会默认禁用部分布局过渡能力
• XML中配置的animateLayoutChanges默认仅开启基础的视图显隐过渡，未开启布局位置变更类过渡，在嵌套滚动容器中极易被系统拦截

解决方案 #

方案1：手动给自定义布局开启完整布局过渡 #

在自定义View的构造方法中手动配置LayoutTransition，替换XML的animateLayoutChanges属性：

// Kotlin 示例
init {
    val root = LayoutInflater.from(context).inflate(R.layout.your_custom_layout, this, true)
    val linearLayout = root.findViewById<LinearLayout>(R.id.deliveryByLayout)
    // 手动创建布局过渡实例，开启所有过渡类型
    val layoutTransition = LayoutTransition()
    layoutTransition.enableTransitionType(LayoutTransition.CHANGING)
    layoutTransition.enableTransitionType(LayoutTransition.APPEARING)
    layoutTransition.enableTransitionType(LayoutTransition.DISAPPEARING)
    layoutTransition.enableTransitionType(LayoutTransition.CHANGE_APPEARING)
    layoutTransition.enableTransitionType(LayoutTransition.CHANGE_DISAPPEARING)
    linearLayout.layoutTransition = layoutTransition
}

// Java 示例
public YourCustomView(Context context, AttributeSet attrs) {
    super(context, attrs);
    View root = LayoutInflater.from(context).inflate(R.layout.your_custom_layout, this, true);
    LinearLayout linearLayout = root.findViewById(R.id.deliveryByLayout);
    LayoutTransition layoutTransition = new LayoutTransition();
    layoutTransition.enableTransitionType(LayoutTransition.CHANGING);
    layoutTransition.enableTransitionType(LayoutTransition.APPEARING);
    layoutTransition.enableTransitionType(LayoutTransition.DISAPPEARING);
    layoutTransition.enableTransitionType(LayoutTransition.CHANGE_APPEARING);
    layoutTransition.enableTransitionType(LayoutTransition.CHANGE_DISAPPEARING);
    linearLayout.setLayoutTransition(layoutTransition);
}

方案2：关闭ViewPager2的过渡拦截 #

给ViewPager2设置transitionGroup=false，允许子布局触发过渡动画：
XML配置：

<androidx.viewpager2.widget.ViewPager2
    android:id="@+id/viewPager"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:transitionGroup="false"/>

代码配置：

viewPager2.isTransitionGroup = false

方案3：替换为手动属性动画（兼容性最优） #

如果以上方案都无效，直接弃用系统animateLayoutChanges，自己实现显隐动画，完全不受父容器影响：

// 显隐TextView的点击事件示例
imageView.setOnClickListener {
    if (textView.visibility == View.GONE) {
        // 显示动画
        textView.apply {
            visibility = View.VISIBLE
            alpha = 0f
            translationX = -20f
            animate()
                .alpha(1f)
                .translationX(0f)
                .setDuration(300)
                .start()
        }
    } else {
        // 隐藏动画
        textView.animate()
            .alpha(0f)
            .translationX(-20f)
            .setDuration(300)
            .withEndAction {
                textView.visibility = View.GONE
            }
            .start()
    }
}

内容的提问来源于stack exchange，提问作者Muhammad Hamza